1. Field of the Invention
The present invention generally relates to an optical device, and more specifically to a multi-channel wavelength division multiplexing/demultiplexing employing at least one microlens, each inserted between two adjacent optical filters along a preset optical path to adjust an optical beam shape and alter a beam waist of a Gaussian beam and an imaging position, thereby greatly increasing optical efficiency of collimators for the whole optical system.
2. The Prior Arts
In the optical application field, some Multiplexing/Demultiplexing module is often needed to implement a Multiplexing/Demultiplexing (MUX/DEMUX) function. For MUX, a plurality of incident light beams are incorporated to generate and output an mixed light beam, and each incident light beam has a different range of wavelength. For DEMUX, one incident light beam with a broad range of wavelength is processed to extract and output a plurality of light beams, each serving as an output light beam and having a different range of wavelength. Particularly, optical filters are generally employed to achieve the above optical function for incorporation/separation, and a plurality of collimators are also collaborated to implement high efficiency of receiving and transmitting the light beam(s).
Further, two MUX/DEMUX modules in the prior arts are commonly used. Specifically, one module is implemented by incorporating a plurality of discrete single channel elements configured in series as shown in FIG. 1A, and the other is through Free Space Optics (FSO) to form a zigzag structure in a free space by combining a plurality of optical filters as shown in FIG. 1B.
For the WDM products manufactured through the technique of the FSO, optical insertion loss primarily comes from collimator misalignment and optical beam shape mismatch. The optical fiber collimator for best fitting to a different distance is used to reduce optical insertion loss caused by optical beam shape mismatch, and more often, a plurality of optical fiber collimators are utilized to fulfill the demand for multi-channel product. However, as the number of desired channels increases, optical insertion loss for a long optical path is not effectively reduced by the optical fiber collimators.
To solve the above issue of collimator misalignment, U.S. Pat. No. 7,212,343 in the prior arts taught a MUX/DEMUX method, as shown in FIG. 2A. One concave lens is placed in the optical path to compensate tilt error of the optical filter, thereby reducing the collimator misalignment. More specifically, the position of the concave lens is at an incident traveling distance, which is close or equal to a reflective traveling distance, such that tilt error due to inserting the optical filters continuously diminishes and optical insertion loss decreases. However, the above skill only works for the concave lens, which is needed to be placed at the position of the ½ distance from the optical filter for optimal performance. Thus, U.S. Pat. No. 7,212,343 is greatly limited in the actual application.
Another solution in the prior arts to solve collimator mismatch issue is disclosed by U.S. Pat. No. 7,031,610, which illustrates a diffraction-compensated WDM (wavelength division multiplexer), as shown in FIG. 2B. The WDM employs the optical filter implemented by a concave lens to reshape the light beam. For the reflective light, the lenses type of optical filter is identical to a concave mirror, which utilizes a curved surface to implement diffraction compensation. In other words, U.S. Pat. No. 7,031,610 uses a filtering element, which specifically has the curve surface, but the position of the filtering element is quite limited by the position of the original filter. Thus, it is difficult to optimize the optical beam shape in the actual application.
Therefore, it is greatly needed to provide a new multi-channel wavelength division multiplexing/demultiplexing device, which employs at least one microlens, each inserted between two adjacent optical filters along a preset optical path, to adjust an optical beam shape of a light beam and alter a beam waist of a Gaussian beam and an imaging position, thereby greatly increasing optical efficiency of collimators for the whole optical system, and overcoming the above problems in the prior arts.